Drive control systems for controlling drives having electrical motors often comprise a DC voltage intermediate circuit from which the electrical motors are supplied with an electrical drive current. The drive current is generally an alternating current, for the production of which from the DC voltage of the intermediate circuit output stage modules or axis modules having an output stage configured as an inverter are generally used.
The electrical energy of the DC voltage intermediate circuit is generally provided from an electrical supply network and is buffered in one or more intermediate circuit capacitors connected to the intermediate circuit. The supply network generally carries a multiphase AC voltage and the process of feeding the intermediate circuit comprises rectification of the AC voltage of the supply network by means of a feed module. The intermediate circuit capacitors are generally arranged in the feed module, the output stage module or in both modules. In order to control a plurality of electrical motors, a drive control system may also comprise a plurality of output stage modules in addition to the feed module.
Drive control systems having a DC voltage intermediate circuit may have, on the one hand, a single-component design, with the result that all modules needed to operate the drive control system, in particular the feed module and the output stage module, are arranged in a common housing of the drive control system. Multi-component designs of such drive control systems are also known, in which the required modules are partially or completely arranged in separate housings and are connected to a common DC voltage intermediate circuit. Such a multi-component motor control system is offered by the applicant as the multi-axis servo system of the series AX8000, for example.
In order to brake an electrical motor connected to the drive control system, the motor can be subjected to generator loading by the drive control system. This is generally achieved by suitably controlling the inverter of the output stage. The electrical energy obtained during generator loading is generally initially stored in the DC voltage intermediate circuit, which results in an increase in the intermediate circuit voltage. The energy obtained and stored during generator loading of the electrical motor can also be used, if the supply network fails, to continue to supply the drive control system with electrical energy until the drive has reached a safe state, for instance is at a standstill. This is described, inter alia, in the document DE 195 09 658 A1.
If the intermediate circuit voltage can no longer be increased further and the intermediate circuit therefore can no longer receive any further energy, the excess electrical energy produced must be discharged in another manner. In addition to destroying the energy produced by the generator in the intermediate circuit, for instance in a resistor connected to the intermediate circuit, the electrical energy produced can also be fed back into the supply network. The feedback function is generally provided by the feed module which supplies the intermediate circuit and is connected to the supply network.